Telstra has stopped remediation work for the National Broadband Network (NBN) amid concern about asbestos discovered at sites in Penrith and Ballarat, but Communications Minister Stephen Conroy has revealed that several sites across the country are also being investigated for the deadly material.

Telstra announced today that it suspended all remediation work and is deploying 200 specialists to NBN sites around the country amid fears that subcontractors may have been exposed to asbestos in legacy Telstra infrastructure being made ready for the NBN.

Communications Minister Stephen Conroy said in Budget estimates hearings on Thursday that the government was treating the matter very seriously, and he had been in constant discussion with Telstra CEO David Thodey over the past few days. The minister indicated that he was aware of other asbestos incidents outside of those already made public.

"I'm aware of an incident in Perth, in which Comcare was called in around a pit in Western Australia which had some very strange findings," he said.

"[And] Senator [Nick] Xenophon has just mentioned a South Australian incident. I'd have to check if there are any others that come to mind."

Tasmania was also identified as having an issue with asbestos, but Conroy said it wasn't clear if actual asbestos was involved in that case.

"There's been claims of a lack of training in Tasmania. I'm not sure that involves any actual asbestos," he said.

Conroy said that most of the incidents involved subcontractors of Telstra, and not NBN Co, but he said that one of the complex issues was that the subcontractors in some areas are doing remediation work for Telstra at the same time as they are constructing the NBN for NBN Co.

"Part of the confusion in Tasmania is that the company that is our subcontractor to rollout the NBN is also the subcontractor Telstra is using to remediate the pits," he said.

"The workforce is fluid between the two."

The minister indicated that further information would be provided when NBN Co executives front the hearing later tonight.

The Communications Electrical and Plumbing Union (CEPU) has called for Telstra to create a fund for workers affected by asbestos, while Telstra has set up a hotline for residents concerned about remediation work in their area.